Ultrafast solid-state glass lasers are frequently mode-locked using a semiconductor saturable absorber mirror (SESAM), which can provide reliable laser self-start and stable mode-locked operation. However, state-of-the-art GaAs-based SESAMs for the 1.55 µm wavelength range require highly strained InGaAs quantum well absorbers with a lattice-mismatch of ≥ 2% relative to the GaAs substrate, which leads to defect formation, reduced damage threshold, and limited design freedom. Here, we present the first fully strain-free SESAMs for solid-state glass lasers at 1.55 µm wavelength, which overcome these constraints. Our devices are grown on InP with a very low residual lattice-mismatch of < 0.1% and incorporate an iron-doped InGaAs bulk absorber. This enables continuous tunability of the SESAM modulation depth and precise control over the ultrafast SESAM recovery time - an unprecedented degree of design freedom. Furthermore, the SESAM structure combines an anti-resonant design with a highly reflective InAlAs/InGaAlAs bottom DBR and a TiO2/SiO2 top DBR, which results in record-low non-saturable losses for InP-based SESAMs of 0.6% for a modulation depth of 0.6%. With this approach, we demonstrate the first stable continuous-wave mode-locked operation of a solid-state Er,Yb:glass laser using an InP-based SESAM. We achieve 224 fs pulse duration at a maximum output power of 102.5 mW and a 79.1 MHz repetition rate, in combination with excellent noise properties of 0.005% integrated RIN over [100 Hz, 1 MHz] and 3 fs integrated timing jitter over [1 kHz, 1 MHz].

Upconversion pumping in rare-earth-doped materials offers access to low-gain and unconventional transitions, unlocking new spectral regions for laser operation. We introduce a scheme for femtosecond pulse generation at 2.3 & micro;m by exploiting photon-avalanche-driven upconversion pumping of thulium-doped crystals at 1.45 & micro;m, combined with a bandgap-engineered GaSb-based semiconductor saturable absorber mirror for self-starting, high-power mode-locking. The upconversion-pumped Tm:LiYF4 laser operating on the 3H4 -> 3H5 transition delivers Watt-level continuouswave output at 2.3 & micro;m, achieving a record optical efficiency relative to absorbed pump power of over 30%, the highest reported for any Tm laser in this spectral range. Stable ultrashort pulse generation that fully exploits the emission profile of the gain medium is further demonstrated, producing 282 fs soliton pulses at a high average power of 478 mW, representing a substantial performance leap over prior demonstrations. These results highlight the strong synergy of optimized upconversion excitation and tailored nonlinear cavity dynamics, establishing a robust platform for nextgeneration ultrafast coherent light sources for molecular spectroscopy and frequency down-conversion. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Understanding nonadiabatic carrier-lattice interactions at the atomic scale remains a fundamental challenge, yet these processes govern energy transfer in materials and ultimately set limits in microelectronics. We combined attosecond core-level transient absorption spectroscopy with many-body theory to uncover how nonadiabatic electron-phonon coupling drives ultrafast relaxations in a titanium-carbide MXene. Phonon-driven changes in carrier localization modulated local field effects (LFEs), yielding carrier-, site-, and orbital-specific absorption signatures. LFEs served as sensitive fingerprints of electron-phonon coupling strength across the phonon spectrum and revealed a breakdown of the Born-Oppenheimer approximation: Electrons lagged lattice oscillations by 32 +/- 8 femtoseconds, whereas holes responded almost instantaneously (7 +/- 7 femtoseconds). Our results establish a framework for probing and controlling nonadiabatic carrier-phonon interactions with orbital and site specificity.

Fiber-coupled terahertz (THz) time-domain spectroscopy (TDS) systems often employ photoconductive antennas (PCAs) as THz emitters due to their high IR-to-THz conversion efficiency. However, their THz power has been constrained to about 1 mW, as fiber-based pulse delivery limits the excitation power to under 60 mW at typical fiber laser repetition rates around 100 MHz. Here, we report the first THz TDS setup that overcomes this limitation by operating at an elevated repetition rate of 1 GHz. We show that the conversion efficiency of InGaAs:Rh-based PCAs is preserved at this one-order-of-magnitude higher repetition rate, resulting in a record emitted THz power of 1.58 ± 0.08 mW for fiber-coupled THz emitters. This significant improvement is enabled by an ultrafast dual-comb optical parametric oscillator operating at 1 GHz repetition rate, delivering two trains of 200 fs pulses centered at 1.55 μm wavelength with up to 650 mW average power. Further pulse compression to 86 fs is achieved using a 2.6 m long fiber delivery to the PCAs, combining dispersion-compensating and standard polarization-maintaining fibers. Using this setup, we demonstrate THz TDS utilizing asynchronous optical sampling at a scan rate of 414 Hz with a peak dynamic range of up to 92 dB at 20 GHz frequency resolution, and 79 dB at 1.1 GHz frequency resolution in 113 seconds integration time.

Developing high-brightness, low-noise supercontinuum (SC) sources is critical for a variety of ultrafast photonics applications. A key challenge in achieving low-noise operation is the suppression of incoherent nonlinear effects and the associated noise amplification. All-normal dispersion (ANDi) SC sources exhibit considerably reduced noise levels compared to conventional soliton-based methods, but their previous lowest-noise demonstrations were limited by amplified spontaneous emission from amplified femtosecond pump laser systems, which seeds incoherent nonlinearities and degrades SC quality. Consequently, the ultimate low-noise limits of coherent SC generation have not been demonstrated by experimental results. Here, we report ultra-low noise, shot-noise-limited SC generation by directly driving the SC process with the un-amplified output of a high-power dual-comb Yb:CALGO oscillator centered at 1053 nm. The resulting SC combs each have a spectrum spanning 820–1280 nm (−20 dB), 1.6 W average power, 1.03 GHz repetition rate, and a comb-line power of ≈10 μW. We conduct detailed noise studies of the SC by analyzing various ≈15-nm-wide spectral bands. All bands reach a shot-noise-limited relative intensity noise below −160 dBc/Hz at 100-kHz to few-MHz noise frequencies. Furthermore, the central spectral bands exhibit an unprecedented noise suppression of the pump laser’s technical noise above ≈2 kHz by >20 dB, which agrees with our semiclassical simulations. Finally, we simultaneously couple both combs into a single ANDi fiber to generate a dual-comb SC with highly symmetric spectra and correlated noise properties between the combs. Coherently averaged linear optical sampling measurements on the dual-comb SC exhibit a high signal-to-noise ratio, showcasing its potential for real-time spectroscopic measurements.

Thulium lasers operating on the 3H4→3H5 transition represent a viable solution for generating broadband emission in the short-wave infrared, at 2.2-2.5 μm, with a potential of supporting femtosecond pulse generation in the mode- locked regime. Upconversion pumping relying on the photon avalanche mechanism is a key technology enabling power scaling of such sources [1], [2]. We report on emission-cross-section limited soliton pulses from a passively mode-locked Tm laser at $2.3 \mu \mathrm{m}$ employing a GaSb-based semiconductor saturable absorber mirror (SESAM).

We demonstrate that for extreme ultraviolet (XUV) transient absorption spectroscopy measurements of thin-film metals, the substrate can significantly contribute to the observed change in absorption even if it is transparent to the pump pulse's excitation wavelengths and does not itself produce a transient signal. When a thin-film tantalum layer deposited on a silicon nitride substrate is irradiated by a near-infrared femtosecond pulse, a coherent acoustic phonon is excited in both the tantalum and the substrate. The substrate response emerges on sub-picosecond timescales and is driven by excitation from the hot-electron distribution in the metal layer. This study underscores the importance of considering substrate effects in XUV transient absorption spectroscopy, which represent a critical factor for accurate modeling and analysis of ultrafast phenomena in thin films.

We report, to the best of our knowledge, the first demonstration of dual-comb operation from a femtosecond optical parametric oscillator (OPO) at a 1-GHz pulse repetition rate. The singly-resonant OPO is fundamentally synchronously pumped by a high-power low-noise Yb:CaF2 diode-pumped solid-state laser, enabling a compact system design, high parametric gain, and stable uniform pulse trains for both the signal and idler outputs. Dual-comb generation is realized in a spatially multiplexed single-cavity configuration for both the OPO and the pump laser. The center wavelength is tunable from 1415 nm to 1645 nm (signal) and 2960 nm to 4085 nm (idler) with average powers up to 650 mW and 200 mW per comb, respectively. The source delivers on average an instantaneous bandwidth of 2.5 THz, a power-per-combline up to 270 µW in the short-wave infrared and 75 µW in the mid-wave infrared is available. We demonstrate the potential of this source for fast dual-comb spectroscopy by detecting ambient methane (∼2 ppm) at 1645.5 nm over a 41-m path length, achieving a normalized spectral signal-to-noise ratio of 42.0 dB Hz1/2. This measurement was performed without any active stabilization.

In this invited talk we present several milestone results that highlight the abilities of our dual-comb MIXSEL technology in the long-wavelength regime.

We report the first demonstration of dual-comb operation from a femtosecond optical parametric oscillator (OPO) at a 1-GHz pulse repetition rate. The singly-resonant OPO is fundamentally synchronously pumped by a high-power low-noise Yb:CaF2 diode-pumped solid-state laser, enabling a compact system design, high parametric gain, and stable uniform pulse trains for both the signal and idler outputs. Dual-comb generation is realized in a spatially multiplexed single-cavity configuration for both the OPO and the pump laser. The center wavelength is tunable from 1415 nm to 1645 nm (signal) and 2960 nm to 4085 nm (idler) with average powers up to 650 mW and 200 mW per comb, respectively. The source delivers on average an instantaneous bandwidth of 2.5 THz, a power-per-combline up to 270 μW in the short-wave infrared and 75 μW in the mid-wave infrared is available. We demonstrate the potential of this source for fast dual-comb spectroscopy by detecting ambient methane (∼ 2 ppm) at 1645.5 nm over a 41-m path length, achieving a normalized spectral signal-to-noise ratio of 42.0 dB Hz1/2. This measurement was performed without any active stabilization.

We demonstrate a spatially multiplexed dual-comb mode-locked Er:Yb:glass solid-state oscillator at 500 MHz. The laser outputs two coherent pulse trains (~40 mW, 230 fs), enabling high-resolution dual-comb spectroscopy without any stabilization.

We present a coaxial dual-comb LiDAR integrated into a laser micromachining station, enabling in-situ 3D profiling of machined parts with sub-micrometer axial precision, offering a cost-effective solution with high precision capability.

Modelocked lasers operating in the 2–3 μm wavelength region are interesting for various spectroscopic applications. To this end, GaSb-based semiconductor saturable absorber mirrors (SESAMs) are developing fast as a practical technology for passive modelocking. Yet, such SESAMs suffer from either too high two-photon absorption or slow absorption recovery dynamics. This study introduces GaSbBi quantum wells (QWs) as a platform to ensure a larger material selection for engineering GaSb-based SESAMs with decreased two-photon absorption and ultrafast absorption recovery time. Three GaSbBi QW SESAM designs were fabricated to compare their performance against conventional GaInSb QW SESAMs. The first structure makes use of typical GaSb barriers and exhibits comparable characteristics to the conventional design, including a saturation fluence of 1.09 μJ cm−2, a modulation depth of 1.41%, and a fast interband recovery time of 6.03 ps. The second design incorporated AlAs0.08Sb0.92 barriers, achieving a reduced two-photon absorption, though at the cost of higher nonsaturable losses due to unintended Bi droplet formation during the growth of the AlAs0.08Sb0.92/GaSbBi QW heterostructure. Importantly, it maintained a fast interband recovery time (30 ps), overcoming the slow recovery dynamics exhibited by standard GaInSb QW SESAMs with AlAs0.08Sb0.92 barriers. The third design explored GaSbBi QWs with higher Bi content targeted for longer wavelength operation at 2.3 μm, which exhibited fast recovery times and good nonlinear reflectivity characteristics. However, the higher Bi content resulted in elevated nonsaturable losses. These results highlight the potential of GaSbBi QWs for short-wave infrared (SWIR) SESAMs, opening the path for further epitaxial optimization to enhance their performance.

Semiconductor Saturable Absorber Mirrors (SESAMs) have revolutionized the ultrafast laser industry. While SESAMs are well-established in the near-infrared regime, using GaAs-wafer epitaxy, there is an increasing interest for the short-wave infrared (SWIR) regime, for which SESAMs can be fabricated using the GaSb material system. Compared to GaAs-based SESAMs, the nonlinear response of GaSb absorbers has been reported to exhibit inherent ultrafast response and a different interplay between the response time and fabrication process. Here we report new advanced features of this interplay in a detailed study investigating the effects of lattice mismatch (e.g. strain) in the quantum wells (QWs), and barrier materials of SESAMs designed for a center wavelength between 2 and 2.4 µm. At 2 μm, SESAMs with ternary InGaSb, GaAsSb, and quaternary InGaAsSb QWs embedded in GaSb were grown with varying levels of QW lattice mismatch (LMM), ranging from compressive strain (-1.7% LMM) to tensile strain (+0.9% LMM). We observed a strong dependence of the recovery time on the QW strain. While a maximum interband recovery time of 340 ps was measured for lattice matched QWs (-0.1% LMM), both compressively and tensilely strained QWs exhibit a shorter interband recovery time. Furthermore, a set of In0.27GaSb QW SESAMs embedded in AlxGa1-xAsSb barriers with different Al content have been grown. We observed that an increasing Al content in the barrier significantly slows down the interband recovery time. All findings are consistent for different heterostructures designed for operation at 2 – 2.4 µm.

Hyperspectral LiDAR (HSL) enables the simultaneous acquisition of the surface geometry and spectral signatures of remote natural targets, making it valuable for various applications such as material probing, automated point cloud segmentation, and vegetation health monitoring. We present a first proof-of-concept study of a broadband dual-comb HSL system based on a 1-GHz dual-comb supercontinuum (SC). The SC spans from 820 to 1300 nm, generated via coherent spectral broadening of a free-running single-cavity dual-comb oscillator at 1053 nm in a single nonlinear photonic crystal fiber. The HSL system achieves a sub-μm ranging precision on a non-cooperative target at an update rate of 670 Hz. The shot-noise limited electronic dual-comb interferograms furthermore encode the spectral information of the target reflection across the SC bandwidth. This allows the capture of precise 3D point clouds with spectral signatures, unlocking new possibilities for spectrum-based material classification.